Tag Archives: multibeam

After a decade of dreaming and years of planning our team of 40 data-hungry geoscientists were given the scent and released from their cages (~desks) with the audacious task of blitzing the whole ice sheet to find samples for dating its retreat. This started in November 2012 in a grey drizzle at Seisdon sand and gravel quarry near Stourport and finished 09:30am 1st August 2015 in bright sunshine when we extracted our last sample, a seafloor core, from the Cleaver Bank in the southern North Sea. It really has been an epic two and half years witnessing the Terrestrial Team with sun-cream in the Scilly Isles to shivers in Shetland, and with dressing gowns in Donegal to JCBs in Norfolk. We really did covered the ground from south to north and east to west and snuck in 28 – yes 28 – different islands of Britain and Ireland, including Scilly Rock and Foula. When samples were not easy to spot and grab, we used radar, seismics and some occasional guesses to work out where to dig with shovel or digger or to core the hidden sediments. It is not quite true that no stone was left unturned, but I have been amazed at how close we got to that, thanks to some amazing levels of energy and motivation; it is indeed lucky that our team displayed traits of obsessiveness and kleptomania when it came to sampling. Bloody well done to all.

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So our very last sample (core 179-VC) on BRITICE-CHRONO has now been collected, marking the end of Cruise Two on RRS James Cook. Even though we never got to shout ‘One hundred and …eighty’ it is more than we had planned. We have sailed, steamed, or dieseled 8971.65 kilometres, taking in Skye, Rona, Shetland, and more North Sea banks including (the infamous Dogger) that you could shake a stick at. We have sampled deep (525 m) and very shallow (19 m), and calm and troubled (force 7). Our ship-track might look erratic to some but, as they say in marketing non-speak, it comprises a subtle blend of caution and well-planned targets with a hint of adventure and wild abandon yielding a truly inspiring collection of mud and sand to sate the yearnings of the most inquisitive discerners of ice sheet curios.

The loot under the care of Team Marine (Lou and Margot)

The haul, now sat in our refrigerated lorry-container and packed in plastic tubes was obtained by lowering our vibro- and piston corers through 18,891.4 metres of seawater and extracting over half a kilometre of sediment (Rich says 542.4 m). As well-known, of course, it is not the length that counts, but the quality. It will be some time however before we know which cores, places and transects yield the best shells and forams for dating, but Margot and Lou have already bagged, sifted and labelled the celebrity shells which we think have the best stories to tell….’well there was this bloomin’ huge great wall of ice that kept crashing down, and would you believe what happened next….’.

Science crew of the RRS James Cook cruise JC123

Thanks to Colm and his science team, the Captain and crew and the geological survey coring teams, and the weather, some good planning, crazy hunches and some luck, this scientific cruise has been a great and enjoyable success. We have a mammoth payload that we hope will provide a legacy of new information for decades. It has been a pleasure having Alex, the ever-present black ninja-photographer on-board, – he stalks, clicks and then runs – in his quest to document our highs, lows and silly moments. Hopefully you have already seen much of his work.

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We set out to do 50 years work in five. Taking this cruise with last year’s, which circumnavigated Ireland, along with our >300 person-days of terrestrial fieldwork we have bagged around 15 tonnes of samples for dating and I hope you agree that we have been around a bit. Sorry if we missed your patch, why don’t you have a go? It is an end of an era for our sampling effort. As project leader, I now breathe a large sigh of relief that it is over and has gone so well, phew and phew again. There is a tinge of sadness though, that we all feel as the fun, bonhomie and making of new friends on hard-won field exploits has now ended. No more pie shops or sneaky pints. Team Terrestrial (Rich and his gang) and Colm’s Marine Crew, can now stand-down to great applause. Derek’s Geochron Team have their work cut out to carefully analyse all the samples and then our Transect Leaders (Tom, Dave, Rich, James, Colm, and Sara) will rise to the challenge of making sense of it all and telling us the story that the shell started to blurt out.

Taking things one day at a time

Chris Clark, signing off on behalf of BRITICE-CHRONO, currently steaming 11 knots, homeward bound, over the Tea Kettle Bank of the southern North Sea. All cores logged and packed and the pinging geophysics finally turned off.

The last week has seen the start of the epic trek north to south from Shetland to the Dogger Bank in the southern North Sea.

We spent the first 2 days looking at some enigmatic grounding wedge features on the sea-floor just west of the Norwegian channel where the British and Norwegian Ice sheets battled it out for supremacy during the last cycle. We also stepped boldly into the unexplored world of outburst floods and drowned coastlines with a some incredible seafloor geomorphology adding to the ice sheet story in relation to the uncoupling of the two ice sheets. Unbelievable geomorph!

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From the Norwegian Channel we headed SW towards the Moray Forth running a 100mile survey and coring transect NW to SE over a spectacular series of moraines before heading into the central North Sea and the urban heartland of the North Sea oil fields around Shearwater and Erskine. Our goal was the Great Fisher Bank (that renowned last bastion of the British Ice Sheet) where we enjoyed a cracking day out sampling Holocene sand and the arrival of a racing pigeon called Terry from Thurso. Needless to say, Terry proved more interesting than the seafloor that day!

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The great odyssey to the Far East was followed by 3 epic days surveying and coring east of the Firth of Forth and then down the east coast from Berwick to Sunderland chasing the imprint of the North Sea lobe. Moraines, deltas, eskers, outwash fans and tunnel valleys littered the bed of the Forth system; all soaked in metres glorious glacial sediment. Better was to follow as we moved south along the Northumbrian coast with the resplendent Whin Sill fracturing the seafloor and grounding zone wedges plastered on to the bedrock. There were also superb, quiet seafloor basins revealing the multi-coloured, muddy barcodes of the deglacial story of the Forth, Tweed and Tyne Ice Streams.

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The final push now. One week to go and on to Dogger Bank for the next two days. Can we prise out the some glacial secrets from beneath that sandy veneer? Huge sand banks seem to guard its peripheral moat warning against trespass, but we are committed now and on to its shallow, upper surface. Our early cores are showing promise; we will see. Hopefully, our target sites in the Humber and Wash area will bring a pot of glacial gold at the end of a cracking month at sea. Then home.

We, the science crew of RRS James Cook Cruise JC123, sailed from Southampton Friday 3rd July bound for the last three transects of the NERC funded Consortium Britice-Chrono, our aim is to work out the timing of the last deglaciation of Britain and Ireland. After a quick stop outside the Solent to test the BGS vibrocore we made hast (10 knots) northwards through the North Sea running geophysical surveys for the North Sea sector (Transect 2) as we went, and in the early hours of Monday 6th July we rounded the northern tip of Scotland on schedule for our speedy (19 knots) tide-assisted passage through Pentland Firth between Orkney and the Scottish Mainland onwards to Transect 8 and the delights of the Minch palaeo-Ice Stream extending north from Skye between the Scottish Mainland and the outer Hebrides towards the edge of the continental shelf and the North Atlantic.

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The Minch seaway ~28-25,000 years ago received ice flow from the major fjords in NW Scotland feeding palaeo-ice stream, which extended north and northwest across the continental shelf. This ice stream dominated the northwestern sector of the British Ice Sheet (BIS). The land- and sea-scape probably developed over multiple glacial episodes, but the sea floor landforms and uppermost geology reflect the most recent deglaciation after 25,000 years ago. The aim of Britice-Chrono is to work out the timescale for this deglaciation, and this has involved fieldwork on land, dating outwash deposits on the Isles of Lewis, Skye and on mainland, and glacially eroded bedrock and boulders across the region. The offshore phase of this research has occupied us, so far, for the last seven days and nights, and involved surveying the sea floor for the morphology and the sediments using acoustic sounding techniques, but critically sampling the sea floor sediments. We have two coring systems on board, a percussive vibrating corer that can sample down to 6 m below the sea bed penetrating the tough materials laid down beneath and in front of former glaciers, and a gravity powered piston corer capable of sampling up to 18m in softer sediments. Our aim is to find shells in these glacial sediments to radiocarbon date and work out the timing of deglaciation.

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The success of the efforts for both our cruises relies on the excellent 24 hour work ethic, diligence and company of the cruise team, science crew, BGS and NOC Piston coring teams and the RRS James Cook captain and crew, all of whom do everything they can to help us. The middle 2-3 days of T8 were particularly nerve-wracking as the BGS crew toiled night and day to fix a particularly truculent problem with the vibrocorer, part of the solution to which lay in finding and removing an electrical break in the 1500 metres of cable that winches the BGS vibrocore to and from the sea bed. Thankfully time was spent obtaining important piston cores in the inner Minch and collecting valuable geophysical data, as the BGS team worked around the clock. As ever in Britice chrono’s experience, the BGS team, had everything needed on board to solve the problem, and cheers greeted the announcement of ready to go, and there followed ‘an in at the deep end’ test of the repair in 500-600 metres of water off the continental shelf fronting the Minch ice stream. Success, with 4.14 metres of glacimarine muds recovered, and on leaving the waters of T8 a further 11 vibrocores were recovered containing the key shell-rich glacimarine and subglacial muds our project requires.

Calm seas, epic sunsets

Looking back on the Minch experience, it is certainly one of the prettiest (former) ice streams we have worked on during the Britice-Chrono cruises, with land in view and visiting the Inner Hebrides passing the Isles of Skye, Lewis/Harris and Raasay amongst others. The leg has been a considerable success, we have collected 1292.6 km of geophysical data (multi-beam and sub bottom profiler), 51 sediment cores (39 vibrocores, 12 piston cores) and 177.2m in vertical sediment profile; who said the Minch was a small ice stream? Our travels have taken us from Raasay Sound in the south over the edge of the continental shelf at 59° 15’ N, and into near shore waters fronting Cape Wrath and the Summer Isles. The answers to the Britice-Chrono geochronological questions must wait on many months of laboratory analysis, but we leave the Minch with all teething troubles behind us, and a growing bounty of cores in the locker. We are ready for the delights of Shetland…!

Leaving the Celtic Sea and the delights of the Celtic Deep, noon on Sunday 27th July, the Royal Research Ship (RRS) James Cook homed in on Britice-Chrono Transect 3 and the delights of the Irish Sea. For me work levels already high increased, with Transect leader duties to fulfil, and the challenges of finding till – glacimarine mud contacts throughout the sector, and do not forget the shells/fossils for the critical dating targets. That said without Katrien’s (van Landeghem) constant input and support it would have been ridiculous, the work in advance of the cruise identifying targets and new locations drew on considerable effort and collaboration focused on this marine sector of T3 over the past 2-3 years. The success of the efforts for T3 obviously relied on the excellent work effort, diligence and company of the cruise team, science crew, BGS and NOC Piston coring teams and the RRS James Cook captain and crew, all whom did everything they could to help us. Not singling people out, but I thank Katrien for constant input, advice and support as co-leader on this transect and Colm as Science Lead on JC106 cruise.

In the Celtic Sea, the ship was home to the friendly academic interplay between James and Daniel, the Irish Sea also offered up a number of longer standing and perhaps more vociferous historical debates! Understanding and interpretation of the nature and extent of glacimarine conditions in the Irish Sea basin has ebbed and flowed for 4-5 decades, with some proponents holding for a full glacimarine ice margin, others subaqueous margins with more restricted access to the ocean and the other end member glacilacustrine basins separated from the sea. For all these views a comprehensive borehole and geophysical survey targeting environments across the sea floor had the potential to advance understanding, but for Britice-Chrono we clearly needed glacimarine conditions and sediments to provide the marine shells and microorganisms that we can radiocarbon date to gain a chronology for retreat of ice from the basin. Marine fossils have been recovered from coastal glacigenic sediment sequences surrounding the Irish Sea for centuries, but debate continues over whether they are in situ or derived, eroded from the sea floor, during ice advance and then redeposited in glacial sediment. If in situ they offer the potential to constrain retreat of ice margins and the development of glacimarine conditions, if derived they cannot really advance our dating control. Some challenging fieldwork and some painstaking analysis of the fossils and microfossils lies ahead.

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Our journey from the Celtic Deep ~ 51°25’N to our first survey and core sites west of Anglesey around 53°15’N took just over 12 hours at a steady ~10 knots. Our first sites, a bit of a late addition and product of general brain-storming, were ~ 13-14 miles west of Holyhead and targeted the deep waters of northern extensions of St Georges Channel. The location kind of bridges T4 and T3, and we wanted some indication of deglaciation of the deep waters between Holyhead and Dublin. On reflection I was not sure what to expect here, but we had planned a sub-bottom profiler SBP and multibeam survey line as an initial exploration, but circumstances and our temperamental SBP conspired against us. The multibeam data on the other hand were excellent, it was a decent trough 2 miles wide 30-40m deep and we used the multibeam to avoid surface sand waves. Our aims were to avoid surface sand and access the underlying laminated glacimarine units, 2.5 hours and two vibrocores later, some success >3m of mud ending in reddish (an Irish Sea glacial signature!) stiff muds. These laminated or bedded sediments hopefully were lain down under marine conditions fronting the ice sheet as the ice margin retreated to higher ground east and north between Anglesey and the Isle of Man.

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From noon 28th July we moved east and north between the Isle of Man and North Wales, and into a region a large part for me where my interest in this research started, working for and collaborating with Geoff Thomas on sections and sediment all around the Irish Sea. In the deeper waters between the Isle of Man and North Wales, our multibeam data gave us a view onto a very well preserved glacial landscape of drumlins and flutes, moulded elongate low hills shaped by the passage of ice. Uncovered as ice melted and then preserved beneath water probably ever since, their summits are grooved with markings probably formed by ice-bergs calving from and then grounding on the landform surface fronting this glacier. Guided by the multibeam sea floor topography and our shallow geophysical data we targeted hollows in the landscape with shallow fills of sediment overlying the glacial surface. Our vibrocorer can penetrate to ~5-6m depending on the sediments, absence of large cobbles or bedrock, heavy seas and luck. Fingers were regularly crossed and the only wooden items in the all metal BGS vibrocorer cabin are now getting quite worn by us touching them for luck and the right sediments. Broadly we divided the Irish Sea basin into four sub areas, 1. South of a line between the Isle of Man and Barrow-in-Furness completed by 21.30 on 30th July, the deeper waters between the Isle of Man and western Cumbria by 18.30 on 31st July, the Solway Firth (between the Isle of Man and Scotland) by 5am 1st August and finally the deep waters west of the Isle of Man by 11.30am 1st August. >500km of survey line, 34 cores in total, almost all of them reaching the reddish glacimarine muds often laminated some with dropstones and in many cores stiff diamicts with clasts typical in character of Irish Sea glacial tills seen in coastal cliff sections around the basin. We had the sediment contexts we desired, the subglacial to ‘glacimarine’ transition and water-lain ice marginal muds from settings across the transect. The nature of this water-body and answers to the Britice-Chrono geochronological questions must wait on many months of laboratory analysis, but I left the Irish Sea northwards for the Malin Sea and T7, satisfied and with the feeling that the sediments and geophysics alone will fill in a significant and long standing gap in our understanding of the last glaciation of the Irish Sea.

Dr. Fabio Sacchetti from the Marine Institute (INFOMAR program) has joined the BRITICE-Chrono survey cruise as Irish Observer and multibeam/geophysical support. As Irish Observer Fabio is overlooking survey operation when in Irish water and makes sure that the survey does comply with Irish standard practices. From a scientific point of view, Fabio has spent the last 11 years mapping the seabed offshore Ireland and the last 4-5 years studying its glacial geomorphology. Back in Ireland Fabio works for the INFOMAR program as hydrographic team leader and onboard the RSS James Cook looks after the multibeam and geophysical data acquisition and processing during the night shift.

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So far the collection of good quality multibeam data has been quite challenging for a number of reasons. The ship is equipped with 2 Kongsberg multibeam systems, the EM710 (for shallow to medium water) and the EM120 (for deep water). The data from both systems are routinely collected day and night and they need to be quickly cleaned and tidally corrected in order to be able to create useful bathymetric surfaces. These info are then used for many purposes including geomorphological interpretation, core site selection and ultimately to make sure that the sampling gear are not deployed over risky seabed. At the start of the survey both multibeam systems had to be calibrated in order to provide the best data quality. After few days and with the weather picking up a bit it was also obvious that the motions sensor (which is needed to precisely correct the swath data) wasn’t performing properly. Further modifications to the standard setup had to be done in order to remove motion artefact that were affecting the usability of the data.

3D image of a canyon head used to calibrate the multibeam systems.

Fabio says: so far this has been an exciting scientific cruise simply due to the sheer amount achieved by the scientists and crew aboard the RSS James Cook, especially in light of anticipated challenges posed by the type of glacial sediment required to be cored, which is proving to be incredibly hard to penetrate. Working with some of the best marine glaciologists in Europe is exciting and challenging at the same time. Data are not just collected but analysed and interpreted on the fly and this contributes to a more hectic, clever, and scientific hands on approach, which makes the all survey way more interesting. It is also a pleasure to see how much projects such as INFOMAR can support and help the scientific communities providing top quality multibeam and geophysical data free of charge, which has been fundamental during the planning of this ambitious research project. The RRS James Cook is an exceptionally good platform for survey and sampling operation with top class facilities and lab space. This is an incredible experience and allows me to learn how things are done onboard one of the best research ship in the world.